The present invention relates to a multilayer printed circuit board, and more particularly, to a multilayer printed circuit board capable of reducing generation of cross-talk noise.
(b) Description of the Related Art
Accompanied with a recent progress in electronic technology, a great need has arisen for fabricating electronic equipment of a high speed and a high performance with a light weight as well as a small size. In order to meet such need, a high density interconnection structure should include wires of a smaller width and finer throughholes. However, in case that signal lines are arranged in a long distance or with the space between them being very small, or in case that electronic equipment itself has a high frequency circuit, a considerable noise is generated in the electronic equipment due to the coupling capacity existing between signal lines. It is generally called cross-talk noise which is generated due to interference between signal lines.
In order to avoid such cross-talk noise, a material having a low dielectric constant may be provided between the signal lines, or a short distance may be provided between the signal lines and the ground plane, both of which will be considerably effective. However, the thickness and the dielectric constant of substrates having a printed circuit thereon cannot be well adjusted to have low cross-talk noise. That is, the coupling capacity between the signal lines is not reduced to a satisfactorily low value so that cross-talk due to the mutual interference between the signal lines may be readily induced, resulting in a reduction in operational reliability of the electronic equipment.
FIG. 1 is a cross-sectional view of a conventional multilayer printed circuit board adopted in electronic equipment. In FIG. 1, two signal interconnection layers 5a and 5b are disposed having signal lines in directions perpendicular to each other with a heat resistant dielectric resin substrate 12 sandwiched therebetween. Besides, ground layers 6a and 6b are disposed so as to sandwich the heat resistant dielectric resin substrates 12 as well as the signal interconnection layers 5a and 5b between the ground layers 6a and 6b.
With the multilayer printed circuit board as described above, if the space between the adjacent signal layers 5a and 5b is small, tile cross-talk noise accompanied by the transmitted signal will be large, resulting in a deterioration of the transmitted signals. For improving such disadvantages, such circuit structure is disclosed in Japanese Patent Laid-Open Publication No. 63(1988)-136694 in which the signal interconnection layers and ground layers are disposed alternately in one layer. With the circuit structure disclosed in the publication, however, a large cross-talk noise will be still induced between the signal lines and between the through-holes in a printed circuit board of a higher density construction. As a result, there arises the problem that satisfactory signal transmission cannot be obtained.
An object of the present invention is therefore to provide a multilayer printed circuit board capable of reducing cross-talk noises between interconnection layers and between through-holes electrically connecting the interconnection layers.